Some users of radio spectrum do not use their allocated frequency bandwidth completely at all times and at all locations; they (sometimes temporarily, sometimes also constantly) leave certain channels unused at given locations and/or during certain time periods. These unused channels are called white spaces. White spaces are most widely discussed at the example of the TV band (i.e. the frequency range between 470 and ˜800 MHz that is used for terrestrial television broadcasting), but the concept is general and could be applied in other bands as well.
White spaces can under certain circumstances be used by other users than the original users. In order to do that it is typically a regulatory requirement for them to operate as secondary users, i.e. to operate (i) without causing harmful interference to the original (these are typically called primary) users and (ii) to accept any interference from the primary users. In order to ensure that no harmful interference is caused, the operational parameters of secondary users are typically subject to regulatory limitations (e.g. with regard to the allowed transmit power, antenna height and other antenna characteristics, etc.). A detailed description of technical and operational requirements of one possible operation in white spaces can be found in CEPT-ECC, Technical and operational requirements for the possible operation of cognitive radio systems in the ‘white spaces’ of the frequency band 470-790 MHz (ECC Report 159), European Conference of Postal and Telecommunication Administrations, January 2011, htttp://www.erodocdb.dk/docs/doc98/official/Pdf/ECCRep159.pdf.
One relevant practical case is that a primary user uses a given channel only in certain locations, and that secondary use is possible outside those locations. In these cases typically no or very little temporal variation is observed.
For this case a promising technical solution to enable white space usage is to use a geo-location database that is able to determine the required operational limitations for one or several secondary users based on information about the users' locations (which is provided to the database as part of a database query). In current regulatory frameworks (e.g. in the US and in Europe) it is foreseen that the database returns a list of locally available channels together with related operational limitations, and it is up to the secondary users to determine how many and which of these channels should be used (i.e. a device can use up to all locally available channels but will normally not do so since devices will be limited in their capabilities, e.g., to simultaneously use non contiguous spectrum chunks).
In this context a cellular network using white space and receiving a range of available channels with associated constraints (such as a allowed transmit power or an expected interference level) has to make an ad-hoc decision how many and which channels to choose. Further, the selected channels shall be allocated to base stations within the cellular network in an optimal or reasonable way.
Accordingly there is a need for techniques which in an ad-hoc manner select channels of a white space for a secondary user. There is another need to assign or allocate the selected channels to base stations of the cellular network in an optimal way.